Bearing Tech Guide

TYPES OF FAILURE

6.7 6.7.1

WIPING APPEARANCE

The bearing surface is severely gouged and distorted. Discoloration of the surface may also be present. The surface also has a colored streaking appearance. See Figure 6-15

Figure 6-15

6.7.2

Example of Bearing Wiping

DAMAGE

Wiping occurs when the bearing and journal have come into direct contact with each other from lack of oil film. Wiping produces high heat from friction between the two surfaces. This condition may be from fuel or coolant diluting of lubricating oil. See Figure 6-16.

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All information subject to change without notice.

7SE448 0102 Copyright © 2001 DETROIT DIESEL CORPORATION

BEARINGS — TECHNICIAN’S GUIDE

Figure 6-16

Illustration of Oil Film Levels

Overloading can cause wiping. Wiping can also occur when the oil galleries become plugged from foreign debris.

6.7.3

POSSIBLE CAUSES

There are several possible causes for the damage: 1. Dilution of the oil by fuel or coolant. 2. Failure to change the lubricating oil within the recommended schedule. 3. Lack of oil pressure from pump, bearing clearance, or plugged oil galleries. 4. Overloading of the engine.

6.7.4

RECOMMENDATION

The recommended maintenance procedures after finding corrosion are: 1. Replace bearings. 2. Change the lubricating oil and fix leaks in coolant of fuel. 3. Use recommended maintenance practices. 4. Clean and flush all oil galleries.



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TYPES OF FAILURE

6.8 6.8.1

LACK OF LUBRICATION APPEARANCE

The bearing layer appears to have been melted with the layer material streaking together. See Figure 6-17.

Figure 6-17

6.8.2

Example of Lack of Lubrication

DAMAGE

The damage is caused by oil flow disruption to the bearing. When the oil flow is disrupted, the bearing and journal come into contact with one another and creates high heat. Without the oil barrier, the bearing layers are melted away. See Figure 6-16.

6.8.3

POSSIBLE CAUSES

There are several possible causes for the damage: 1. Using the wrong type of oil. 2. Not performing the daily maintenance practice on the engine. 3. Failing to change the lubricating oil within the recommended schedule.

6-20




6.8.4

RECOMMENDATION

When lack of lubrication occurs, replace bearings. 1. Replace bearings. 2. Check all other engine parts for similar wear. 3. Use recommended maintenance practices. 4. Change lubricating oil within the recommended interval.



6-21

TYPES OF FAILURE

6-22




GLOSSARY Aluminum Contamination

Failure of aluminum components in an engine, contributing aluminum debris into the lubrication system; i.e. blower(s), intermediate camshaft bearings, flywheel housing, turbochargers, piston skirts, oil pump housings, and governor housings.

Bearing Alloy

Any alloy that is used as a bearing lining surface.

Bearing Cap

The removable half of the housing that holds the bearing shells in place.

Bearing Corrosion

Chemical attack evident on bearing surfaces by metal loss or discoloration.

Bearing Material Fatigue

The cracking and eventual “chunking out” of bearing material associated with repeated loading in excess of the fatigue strength for the material.

Bearing Lining Material

Trimetal alloy mainly of copper with lead and tin for maximum fatigue strength.

Bearing Lower (Half Shell)

The bearing half that is made for assembly in the bearing cap.

Bearing Housing Bore

The housing into which the bearing shells are assembled.

Bearing Upper (Half Shell)

The bearing half that is made for assembly in the engine block or connecting rod as opposed to the bearing cap.

Bearing Wall Thickness

The dimension of the bearing shell through the radial cross section as measured by a micrometer with ball attachment.

Bore (Housing)

The inside diameter of the main bearing/connecting rod bore into which the bearing shells are assembled.

Bore Geometry

Bore diameter, roundness, taper, and alignment (main bearing).

Cavitation Erosion

Cavitation is the formation of bubbles in a fluid (lubrication oil) which may occur when the fluid is subjected to low pressures. The high energy dissipated when these bubbles collapse near the bearing surface causes gradual erosion and pitting of the surface. This



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GLOSSARY

condition is called cavitation erosion and is generally not harmful to bearing performance. Clearance (Diametral Bearing)

The difference between the bearing housing bore ID and the bearing journal OD.

Connecting Rod

The structural member that transfers the force from the piston to the crankpin.

Connecting Rod Bearing

The bearing at the big end of the connection rod in which the crankpin rotates.

Copper Exposed

A condition where the bearing shell has been worn through the overlay and into the copper bearing lining as evidenced by a copper color.

Corrosion

See Bearing Corrosion.

Crankcase

The enclosure for the crankshaft formed by the oil pan and the lower portion of the engine block.

Crankpin

The crankshaft journal around which the connecting rod bearing shells are installed.

Crankshaft

The main shaft of an engine; contains the main bearing journals and crankpins.

Crown

The center area of a bearing shell.

Crush

The circumferential interference fit necessary to hold two bearing halves securely in the housing bore. In a bearing half, the amount of circumference in excess of a half circle.

Crush Relief

Metal removed on the bearing surface at the parting faces extending the full width of the bearing.

Debris

See Foreign Material.

Dirt

See Foreign Material.

Dilution

Either fuel or coolant in the lubrication system mixing with the lubrication oil.

Edge Loading

Unequal loading of a bearing shell evidenced by taper wear across the length of the bearing.

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Embedability

The ability of the bearing material to absorb foreign material without causing serious bearing damage.

Embedded

The enclosure of solid particles into the surface of a bearing shell; i.e., dirt, shavings, metal grinding dust.

End Clearance (End Play)

The possible forward and backward movement of the crankshaft in the main bearing fore or connecting rods on the crankpin.

Engine Block

The main casting of an internal combustion engine containing the cylinder bores and main bearing bores.

Fatigue

See Bearing Material Fatigue.

Fatigue Strength

The ability of a bearing material to withstand the repeated loads during engine operation.

Foreign Material

Any extraneous material not intended to be present, i.e., particles of steel, cast iron, dirt sand, etc.

Free Spread Diameter

See Spread.

Hot Short

This term is used to describe a condition where the bearing lining becomes unbonded from the steel bearing back because of an excessively high bearing temperature. The high bearing temperature is almost always a result of the heat generated during a scoring failure. This condition does not indicate an initial defective bearing lining to steel back bond. It merely indicates that a high bearing temperature was reached during a scoring failure to “hot short” or “melt” the bond layer.

Hydraulic Erosion

The eating away of the bearing overlay by the action of the oil flow past the surface.

Insufficient Lubrication

Inadequate flow rate of the lubrication oil for satisfactory performance.

Journal

The part of a shaft that revolves in a bearing.

Limit

A size dimension either plus or minus the tolerance (high or low limit).

Line Bore

To machine the crankshaft main bearing bores, creating bore centers which fall on a true center line.



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GLOSSARY

Lining

See Bearing Lining Material.

Lining Fatigue

See Bearing Material Fatigue

Locating Tang

A projection on a bearing back that locates in a machined slot in the bearing seat, used to locate the bearing in the housing bore and keep it from moving laterally.

Lubricant

A substance capable of reducing friction between mating surfaces in a relative motion through separation by an oil film.

Main Bearing

A bearing that is used to support the crankshaft in the cylinder block.

Main Bearing Journal

A crankshaft journal that is supported by a main bearing.

Main Bearing Saddle

The area in the cylinder block machined to receive the upper main bearing.

Normal Wear

The amount of bearing wear experienced during normal engine operation.

Oil

A viscous fluid, insoluble in water.

Oil Clearance

See Clearance — Diametral Bearing.

Oil Film

The thin layer of oil that protects the journal and bearing surfaces by separating them and preventing journal to bearing contact while the engine is in operation.

Oil Gallery (Main)

The main oil supply line in the engine block, often referred to as the header. Oil flows from this major supply route under pressure to the many parts that are to be lubricated.

Oil Groove

A canal machined in the surface of a bearing to spread oil on a friction area or to permit the transfer of oil to another part.

Oil Hole

A hole drilled through the bearing wall or crankshaft journal to allow the passage of the oil.

Oil Starvation

A condition of inadequate oil flow or supply.

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Out of Round

An inside or outside diameter, designed to be perfectly round, having varying diameters when measured at different points across the diameter.

Overlay Checking

The bearing overlay cracking which indicates the beginning stages of overlay fatigue.

Overlay Fatigue

The cracking and eventual lose of overlay material associated with repeated loading in excess of the fatigue strength of the overlay material.

Overload

A bearing load in excess of the load the bearing was designed to carry.

Oversize

Either an inside or outside diameter that is greater than the standard size.

Parting Edge

The edge formed where the inside or outside surface of the bearing joins at the parting face.

Parting Face

The surface that is in contact with the other bearing half when the bearing is assembled.

Parting Line

The theoretical line formed by the contacting parting faces.

Spread

The excess of diameter at the outside parting edges in the free state over the housing bore into which the bearing is to be installed.

Spun Bearing

A bearing set which has adhered to the journal and turned in the bore for various reasons, i.e. dirt, lack of lubrication, or improper lubrication.

Tolerance

An acceptable range of dimensions to provide accuracy in finished parts.

Thrust Bearing

A flat bearing used to control the crankshaft end play.

Undersize

Either an inside or outside diameter that is less than the standard size.

Wear

The gradual decrease in bearing thickness.



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Bearing Tech Guide

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